First, items are not equipped from the inventory, they are equipped from the Items button on the Position screen.
Second, if you are encountering an error with the website, I suggest making a report on the Bug Base, with is the "Bug Report Form" link at the bottom of your right side menu. Be aware you will have to create a separate account - it doesn't import from the main SWC database.
____________"May the Grace of Ara go with you, and His Vengeance be wrought upon your enemies."
Only fools and children dream of heroes.